CONTRIBUTIONS TO THE GEOLOGY OF BENGUELLA. 



505 



The general character of this series of gneisses is remarkably similar to that of 

 the biotite-gneisses in the Lewisian of North-Western Scotland. 



The strike is generally between 55° and 60° (about N.E. by E.). 



Above the Lengwe Gorge the railway continues to rise steeply past a series of 

 cliffs of gypsiferous sandstone. This bed rests on an eroded surface of gneiss, as at 

 km. 52*1, at the height of 413 feet (fig. 4). The sandstones are here irregularly 

 bedded, and contain alternations of soft sandstone or sand-rock with layers of loam. 

 Some of these bands are cut through by small slip faults. A band of conglomerate 

 is interbedded in this sandstone. Some of the sandstone bands end off abruptly 

 against vertical steps in the gneiss. One band contains some obscure impressions 

 which may be organic in origin, but I found no determinable fossils. The best clue 

 to the age of this rock is that some of the bands are full of wind-rounded grains. 

 The material is very different lithologically from that of the Cretaceous rocks, and 



Fig. 4. 



it was probably deposited under different climatic conditions. These subaerial 

 sandstones are probably Mesozoic but of pre-Cretaceous age. 



The gneiss series is again exposed east of the station of San Pedro. The first 

 notable railway cutting is at km. 55, and the rocks there are biotite-schist and a 

 regularly banded gneiss. The foliation is vertical, and the rock is traversed by 

 pegmatite veins and horizontal faults. The strike is to east-north-east. Some of 

 this rock, by its even banding, low proportion of felspar, and arrangement of the 

 biotite, resembles the Moine Gneiss of Scotland, though owing to its vertical foliation 

 and conditions of weathering the characteristic flaggy structure of the Moine Gneiss 

 is not developed. 



Three kilometres beyond this exposure and shortly beyond Monte Sahoa occur 

 the first outcrops of the granites, which are the predominant rock from 58 km. to 

 the bridge across the upper Catumbella River at km. 272. The granites form a belt 

 of desert country which formed the great obstacle to communications between the 

 coast and the better-watered highlands of the interior. The railway enters this 

 desert on a course to the south-south-east. The level gradually rises from 790 feet 

 at km. 54 to 2970 feet at km. 95. The chief features in the scenery are the numerous 



